When you call your friend and the phone is switched off or out of the carrier’s reach, you know that instantly.
With global messaging using A2P messaging platforms, it is much more complicated, as most of the heavy lifting is done without you knowing it. Here are the main reasons SMS messages go undelivered.
1) The phone is switched off or out of the carrier's reach
If you get a busy signal while calling, you can try again later or just give up. When the SMS doesn’t get delivered on the first try, it is automatically re-sent in certain intervals without you knowing it. So, when the phone is available again, the message still gets delivered.
Note: Messente's system is configured to try to deliver messages within 6 hours. When the message still fails, it is marked as 'Failed.'
2) False negative
Sending SMS messages also requires receiving Delivery reports (DLR) from carriers or operators. When the operator fails to respond with the correct receipt, the sender isn't notified of the delivery and marks it as 'Failed.'
NB! USA, Canada and most Latin-American countries are known not to provide delivery reports at all.
3) The number is roaming (abroad)
Sending an SMS to a number that is currently not in the home-country often causes lots of problems, and therefore, delivery to numbers that are roaming is not guaranteed.
4) The sender you are using is prohibited
Some countries or operators are blocking some types of senders or A2P messaging platforms. Japan, for example, doesn’t allow sending A2P SMS messages from regular phone numbers. Telia Sonera in Finland, on the other hand, is blocking messages from alphanumeric senders like “CarService1″ or “BestHotel."
5) The carrier is blocking the SMS
Operators are also known to block some SMS routes from time to time. This also requires SMS services to re-route the message via another working route, which can cause temporary delivery issues.
6) Local regulations restrict SMS messages
In some countries, local regulations restrict sending SMS messages, for example in some countries, messages marked down as marketing can be sent only during workdays from 8 am to 8:30 pm.
7) The number might be in the Do Not Disturb list
In some countries, the operators have a list, where handset owners can add their numbers by themselves so that no messages from an A2P connection can reach their numbers.
8) The handsets settings may have the SMS messages turned off
In certain cases, there may be conflicts between different applications that may receive SMS messages. This may cause one or all of the applications not to receive messages due to their SMS receiving capability turned off.
Also, there is a possibility of the default application staying in the position of not receiving the messages after a conflicting application has been removed
9) Conflicting SMS applications
Sometimes different applications on the handset can receive SMS messages and due to their conflicts, the messages are not being correctly received by the handset as the applications are conflicting and the message is not able to deliver to any of them resulting in a failed message.
10) The carrier is experiencing technical difficulties
In some cases, however, all can come down to the simple point that the carrier (or more specifically the hardware involved) is having some technical difficulties and messages are just not able to be delivered.
We have seen in the course of years all manners of different happenings, from the servers having a critical error to an accident in construction, which has resulted in the major data cable being cut.
Conclusion
As you can see, there can be quite many reasons why your message has gone undelivered. Hopefully, this list can clear up things a bit and sometimes even prevent undelivered messages from happening.